This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We would like to continue the calculations of interactions between nucleic acid bases in a CpG step upon hydrogenation at N3 position of guanidines. Our calculations with a small, 3-21+G, basis set indicate that guanidines from opposite strands may be cross-linked. Completion of the calculations with larger basis sets will require further time allocation. In addition, we would like to explore the role of methylation of cytosine in CpG steps and to perform calculations for a TpA step.